the cap is not only there to combat lag, but also to make sure gameplay is not negatively impacted?

That's true, but it's sort of a mix of things, gameplay is still dependant on hardware, and “lag” is often used to report many different issues that players don’t know how to accurately describe.

Design has a lot to do with imposing limits, whether it’s the amount of items you can stack in your inventory, the amount of quests you can have at the same time, the amount of dailies that reset every 24h, the amount of main spells that each class should have in their “rotation”, the amount of players that should be in a raid, arena, or bg, or… the amount of players that can connect to a specific realm.There's a "sweet spot" and a limit for everything.

So before suggesting or demanding anything, I recommend waiting for the results of Connected Realms.

Exactly, hopefully Connected Realms will help out a lot, lower populated realms will get some love and players will (hopefully) stop flocking in to the highest populated realms and causing queues during patches/expansion launches. But please do continue to suggest ideas though, those are always welcome.

We have opened FCMs for all the realms that are having high queues at the moment.Unfortunately not that many players seem to use them. Players seem to perceive the destination realms for FCMs as if they were the lowest populated ones, they’re not. Now, I’m not sure if this is due to players checking up realm populations on 3rd party websites or if it’s just because players expect the destinations to be bad ones by default. If you check some of them, they’re really not, very far from it.

For quite some time now, we have been trying to give you much more popular destinations to help with the queues on the most popular realms. There is also another issue at play here though, and I'm sure everyone is aware of this, it's quite normal human behaviour, players having high queues see FCMs open and always expect that others will move but not them, and if everyone thinks exactly the same way, guess what happens...

For most of the FCMs we have opened recently, we have at least 1 FCM for each source realm that has a medium/high populated realm set as destination, and often those are some of the most balanced realms in terms of faction ratio under the same realm type. (yes, PvP realms tend to be slightly more prone for horde domination, and alliance for PvE, that’s player group behaviour, not much we can do about that with simple FCMs)

For example, for the English FCMs you have at least these four realms, Aggramar, Auchindoun, The Maelstrom, and Darksorrow. Not only these are actually very decently populated realms (obviously these are not the highest ones, as we don’t want to create queues on other realms), but they are also quite balanced in terms of faction ratio, particularly Darksorrow and Auchindoun.

Not all destinations can be like these, we know that. But some are, and I just want to make sure that players are aware of this and do not miss the opportunity to migrate and escape the queues by some weird perception issue that they might have with FCMs destinations never being good ones, when in fact they are usually much more popular and diverse destinations than the ones we used to provide in a distant past.